This application relates to shaped plastic lenses and to a method for their manufacture. More particularly, the application relates to plastic lenses having substantially no optical power, high impact-resistant and abrasion-resistant properties and to a method for forming such lenses wherein a high scratch-resistant convex surface of the lens is formed in situ during the method.
Curved light-polarizing laminates useful as lenses and comprising a layer of a molecularly-oriented light-polarizing material arranged between a pair of substrate sheets are well known. It is known to manufacture composite light-polarizing lenses, which include a layer of an optical quality polymeric material on each side of a shaped light-polarizing member. U.S. Pat. No. 3,940,304 describes a technique, which includes in situ polymerization of the optical quality polymeric material layers in a mold. An optical quality monomeric material is inserted into a shaping mold so as to cover both surfaces of the light-polarizing member and heat is applied to cause polymerization of the monomeric material to occur thereby resulting in the formation of a composite polymeric light-polarizing lens structure.
Further, it is known to make lenses, which have substantially, no optical power by shaping a composite lens, blank in a mold. For example, U.S. Pat. No. 5,434,707 teaches a method for forming shaped plastic lenses having substantially no optical power and comprising a laminate of a light-polarizing layer arranged between a pair of thermoplastic substrate sheets. According to the method, the composite lens blank is inserted into a mold which has heated curved platens and subjected to heating and pressing such that the thermoplastic substrate sheets are deformed and rendered flowable with the result that there is produced a composite lens which has substantially no optical power. The method requires lens-forming platens having predetermined radii of curvature which make possible, under the heating and pressing conditions, the production of plastic lenses of non-uniform thickness, that is, lenses which are thickest in the central region and of diminishing thickness radially to the periphery thereof. Although the method taught by the '707 patent provides shaped plastic lenses having substantially no optical power and of good durability, it is not completely satisfactory for all situations.
As the state of the art advances, efforts are made to provide new plastic lenses, which can meet new performance requirements, and to reduce or eliminate some of the undesirable characteristics of the prior art materials. For example, there is a continuing demand for high impact-resistant, plastic lenses, which have substantially no optical power for various uses such as in sporting events. However, simply making high impact-resistant plastic lenses by shaping in a mold a lens blank made of a high impact-resistant plastic material is not completely satisfactory since such high impact-resistant materials typically exhibit high optical stress properties and tend to develop cracks under the heating and pressure conditions required to shape the lens. Thus, it would be advantageous to have a method for making shaped lenses which have substantially no optical power and high impact strength and which are suitable for use in eyeglasses. It would also be advantageous to have shaped lenses which have substantially no optical power and which possess a high scratch-resistant convex surface.